The source of functional pancreatic islets is one of the main factors limiting islet transplantation. The goal of the proposed project is to develop a technology to expand adult human pancreatic islets. The expected final result will be a well-characterized, immunologically-defined population of expanded human islets that could satisfy the needs of transplant surgeons. The procedure will be based on our preliminary data on expansion of adult porcine islets and will be done in two steps - cell proliferation and cell differentiation. Cells will be expanded on the extracellular matrix protein laminin-5 in medium conditions to be optimized for human islet. For differentiation a procedure designed for porcine islet cell aggregation will be adapted for human islets. The primary objectives will be to obtain adequate cell growth and induce rapid restoration of insulin expression during the aggregation phase, as well as in vivo functionality, rescuing induced diabetes in immunodefficient mice. A profile of markers including islet hormones and cell type specific markers, will be developed to characterize the cells at different stages of proliferation and differentiation. These results will provide a proof of principle for the human islet expansion technology and will allow the commencement of large animal experiments as a next step to the clinic.